Variable Frequency Drives

Variable Frequency Drives (VFD's)

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Variable Frequency Drives (VFD’s) enable speed control for three-phase AC motors such as those in HVAC systems, conveyors, fans, and pumps. VFD’s drive an electric motor by varying the frequency and voltage supplied to the unit.

If an application does not require the motor to run at full speed, the VFD can ramp down the frequency and voltage to meet the load requirements of the electric motor. As the requirements of the application change, the VFD can simply turn up or down the motor speed.

Electric motors have a longer lifespan if they are only running when and how they need to be, and the energy savings are extremely significant.

Installation #1: Senior Living Facility and Rehabilitation Center

Situation: At this 270,000 square foot facility, a large Water Source Heat Pump System needed to be optimized.

Solution: We installed 28 Variable Frequency Drives along with an Energy Control System to regulate air handler and cooling tower fans, pumps, and motors. This implementation was acknowledged as a TVA Top 3 VFD Install for 2016.

Savings: Average monthly savings were over $7,000. Over 912,000 kWh’s were saved during the first year. The chart below details the savings.

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Installation #2: A federated farm supply cooperative serving 164 retail outlets

Situation: In the 53,000 square foot Main Office are two HVAC chilled water systems:

includes a 90-ton Carrier air-cooled chiller with a chilled water pump (7.5HP), three constant volume air handlers (7.5HP, 5HP, 15HP), and an accompanying return fan (1.5HP).
includes a 60-ton air-cooled chiller with a constant GPM chilled water pump (5HP) and one constant volume air handler (25HP).

Solution: We installed Eaton variable speed drives (VFDs) on all the above designated items, and an Energy Control System. A central controller resides wirelessly on the customer’s internet router, enabling remote access and communication with the VFDs via a Modbus network.

VFDs, when added to constant volume air handling fans, create a hybrid variable volume air handler system. Fan VFDs operate at full speed when the outside air temperature is at or near summertime design conditions. The speed is reduced via an algorithm as the outside air temperature reduces throughout the year. This saves energy and improves dehumidification.

The Energy Control System includes an Unoccupied Off status on a daily and weekend schedule. During Unoccupied Off, air handlers are off, but start hourly to create air flow to monitor room temp, and change to Unoccupied On status if the room temperature rises above 80 or below 60. AHU’s run at 50% speed during this condition.

CHWP-1,2: These pumps reduce speed based on chilled water supply and return water temperature differential.

Sensor inputs: Supply Water Temperature, Return Water Temperature.

AHU-1,2,3,4: Air Handlers reduce speed as outside air temperature falls.

Sensor Inputs: Outside Air Temperature (provided by an API from a weather website and updated every 3 minutes), Room Air Temperature.

RF-4: Return fan associated with AHU-4

Return fan to track AHU-4 at the same speed output less 5%

Effective Change in Power as the Speed of motors driving fans and pumps is reduced

Savings: March 2017 through March 2018
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ROI: 72.3 %
Simple Payback: 17 Months
There are 8,300 out of 8,760 hours per year below 90 F degrees. The system is saving energy 95% of the year.
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Installation #3: A plant that manufactures automotive components

Situation: 100% outside air building pressurization unit for a clean room manufacturing process. The unit has a 50hp fan, chilled water coil and gas heater. The fan runs at full speed regardless of exhaust fan capacity or room pressure.

Solution: we added a 50 hp Eaton Variable Speed Drive (VFD) with customized Thermal Dynamic energy controller. The fan speeds up and slows down to track a room pressure setpoint of .015”. As the processes engage or disengage their exhaust fans the VFD provides the correct amount of air to the System.

Savings: The chart below shows the Marelli (Calsonic) kWh usage and savings through May 2020. There were also savings in demand charges, chilled water costs, and heating gas charges.